Among engines mounted on a vehicle, there are engines in which cylinders are arranged in series, another engine in which cylinders are placed opposite to each other, and also a V-shaped engine in which cylinder banks are arranged in a letter V-like configuration.
In some of the above V-shaped engines, first and second cylinder heads are respectively placed on first and second cylinder banks of a cylinder block, and a bearing cap for supporting a crank shaft in cooperation with the cylinder block is attached to a lower part of the cylinder block. In the V-shaped engines, in order to install auxiliary devices such as a compressor and a power steering pump for an air-conditioner, the cylinder block is further provided with a bracket for mounting the auxiliary devices thereto and also with a mounting bracket for supporting an engine on a vehicle body.
As one example of the intake system for an engine, there is a system disclosed in a published Japanese Patent Application No. 60-62654. The intake system for a V-shaped engine disclosed in this publication is constituted such that an intake passage for the V-shaped engine comprises two surge tank portions formed by surge tanks integral with upper portions of branch paths branched off from the surge tanks, and a crossed-manifold portion in which the branch paths extending from opposite sides are alternately intersected at their downstream portions, and walls constituting the branch paths at the crossed-manifold portion being commonly possessed by and between the adjacent branch paths, each of the branch paths at the crossed-manifold portion being provided with a fuel injection nozzle, the crossed-manifold portion being tightly secured to the two banks by fastener means extending through the adjacent branch paths, thereby enhancing attachability and attaining a compact dimension of the intake path.
As shown in FIG. 3, in the conventional intake system for an engine, a V-shaped engine 102 comprises first and second cylinder heads, not shown, placed respectively on first and second cylinder banks 106-1, 106-2 of a cylinder block 104, first and second head covers 108-1, 108-2 being provided respectively to the first and second cylinder heads, a bearing cap, not shown, being attached to a lower part of the cylinder block 104, and an oil pan (not shown) being attached to a lower part of the bearing cap. A crank shaft (not shown) is rotatably supported by the cylinder block 104 and also by the bearing cap (not shown) in a forward and backward direction relative to the engine 102.
The engine 102 comprises, for example, six cylinder units, three on one side and the remaining three on the other side, and an intake path communicating with those cylinder units. A throttle valve, not shown, is disposed within a throttle body 112. An intake pipe 114 is connected to an upstream side of the throttle body 112, and a downstream side of the throttle body 112 is branched into first and second branch paths 118-1, 118-2 by a branch tube 116. First and second surge tanks 120-1, 120-2 are connected respectively to downstream side end portions of the first and second branch paths 118-1, 118-2. The first surge tank 120-1 on one side is connected to the cylinder units on one side through first to third intake tubes 122-1 to 122-3, while the second surge tank 120-2 on the other side is connected to the cylinder units on the other side through fourth to sixth intake tubes 122-4 to 122-6.
The intake path 110 comprises the intake pipe 114, the throttle body 112, the branch tube 116, the surge tanks 120-1, 120-2, and the first to sixth intake tubes 122-1 to 122-6. The first and second surge tanks 120-1, 120-2 are communicated with each other through a communication path 124.
When the intake pipe 114 is placed between the first and second cylinder banks 106-1, 106-2 in such a manner as to extend under a lower part of the communication path 124, it has a predetermined space, as shown in FIG. 4, relative to the first to sixth intake tubes 122 and the communication path 124. The intake pipe 114 is firmly secured to the first to sixth intake tubes 122-1 to 122-6 by fixing bolts, not shown. As a consequence, it is practically impossible to set the configuration and diameter of the intake pipe large. Since the intake pipe cannot be made large enough in diameter, intake efficiency is bad. This is disadvantageous in view of practical use.
If the diameter of the intake pipe is set large enough in order to enhance the intake efficiency, it becomes necessary to increase the space between the first and second cylinder banks as well as the space relative to the lower part of the communication path in order to allow the passage of the intake pipe. The arrangement for firmly securing the intake pipe to the first to sixth intake tubes brings about such inconveniences that a span for mounting is increased and the mounting areas are reduced in strength.
According to the present invention, in order to obviate the above inconveniences, there is provided an intake system for an engine, which intake pipe is connected to an upstream side of a throttle valve of the engine having first and second cylinder banks of a cylinder block formed in a V-like configuration. The intake path, at its intermediate part downstream of the throttle valve, is branched into first and second branch paths by a branch tube, and the first and second branch paths are provided at their downstream end portions with first and second surge tanks, respectively, the first and second surge tanks being connected to each other through a communication path. An upper portion of the intake pipe is disposed between the first and second surge tanks and under the communication path and is firmly secured to the communication path.
With the above-mentioned construction of the present invention, when the intake pipe is placed between the first and second surge tanks in such a manner as to extend under the communication path, an upper part of the intake pipe is firmly secured to the communication path, thereby enabling an increase in the diameter of the intake pipe to the extent good enough for intake efficiency while enabling the providing of a compact system.